Devices, e.g., tablets, smart phones, laptops having a touch screen, etc., are increasingly being used in connection with a pen or stylus (hereinafter these terms are used interchangeably) as an input modality. Certain inputs are possible using a completely passive pen, i.e., where the pen itself is not actively transmitting information but simply serves as an implement to provide contact with a screen—similar to a finger input. Other pens are semi-passive in that they transmit data, e.g., location data, but in a reactive manner, e.g., in response to a transmission. Still other pens are so-called “smart pens” that actively transmit input data, e.g., location data, other input data (e.g., button press data, pen status data, etc.) from the smart pen to the device.
No matter the type of pen, a visual display output is provided in response to the pen input. For example, in a handwriting application, the handwriting display output is provided in response to the pen input of handwriting. In this way, a user may visualize what he or she has done with the pen, in this case, providing handwriting.
When writing with an electronic pen on a device that has the display output and the pen input surface co-located (e.g., layered one on top the other), such as commonly found in a tablet computing device or the like, inevitably there is some visible offset between where the pen contacts the writing surface and where the “ink” point (i.e., the display output) appears on the display, e.g., underneath the glass. Most often, the tablet is sitting flat on a table in front of the user, and the user is seeing the display from an angle. In this configuration, the thickness of the cover glass creates parallax. Positioning errors from the pen sensing system contribute further, altogether breaking the illusion that writing digitally is anything like writing with a pen on paper.